Heat exchanger supporting means

ABSTRACT

A heat exchanger comprising serpentine finned tubes disposed in an annular configuration, with means for positioning and supporting the unfinned return bends of the tubes in such a manner as to prevent coolant fluid from bypassing the finned portions, and to allow movement of the tubing in thermal expansion.

United States Patent [151 3,701,381 [451 Oct. 31, 1972 Watts [54] HEAT EXCHANGER SUPPORTING MEANS [72] Inventor: l-largus Watts, Hawthorne, NJ.

[73] Assignee: Curtlss-Wright Corporation [22] Filed: July 21, 1971 [21] Appl. No.: 164,556

[52] US. Cl ..l65/82, 165/162, 60/3951 R, 60/3932 [51] Int. Cl. ..F28! 13/00 [58] Field of Search....l65/55, 69, 81, 134, 164, 169,

[56] References Cited UNITED STATES PATENTS 2,057,299 10/1936 Foss ..l65/l35 2,268,360 12/ 1 941 Walker ..165/174 2,569,446 10/ 1951 Bonvillian et al ..60/39.32 3,379,244 4/1968 Gilli 165/1 63 Primary Examiner-Frederick L. Matteson Assistant Examiner-Theophil W. Streule Attorney-Raymond P. Wallace et a1.

[57] ABSTRACT A heat exchanger comprising serpentine finned tubes disposed in an annular configuration, with means for positioning and supporting the unfinned return bends of the tubes in such a manner as to prevent coolant fluid from bypassing the finned portions, and to allow movement of the tubing in thermal expansion.

5 Claims, 6 Drawing Figures v 1 HEAT EXCHANGER SUPPORTING MEANS BACKGROUND OF THE INVENTION Regenerative heat exchangers in turbine engines are known, in which one heat exchanger is disposed to extract heat from the exhaust gases of the turbine, and then transfers its coolant to another heat exchanger disposed upstream, which givesup the heat to the incoming air. Such heat exchangers are commonly annular in configuration, having a plurality of passes of serpentine tubing longitudinally disposed within the annulus, with the bights of the serpentine extending back and forth across the annular space between the inner and outer diameters of the annular space. In order to completely fill the annulus, the convolutions do not extend radially thereacross, but are curved so that the passes of tubing are arcuately stacked in a nested relationship around the annulus.

When the tubes bear heat-dissipating fins, a problem arises of possible interlocking of the fins of adjacent passes, with possible damage to the fins owing to thermal movements of the tubing. Also, it is not possible to provide fins on the bends where the tubes reverse direction, so that a considerable proportion of the flow of fluid across the tubes may bypass the finned portion and flow across the ends where it is less effective in heat transfer. These problems are solved by the present invention.

SUMMARY This invention relates to regenerative heat exchangers for turbine engines, and more particularly to means for positioning and spacing finned tubing in an annular heat exchanger in such a manner as to allow thermal movement without interlocking and damage to the fins, and to prevent loss of effectiveness by fluid flow across unfinned portions of the tubing.

This is accomplished by clasping each of the return bends of tubing in an elongated clevis member brazed to the tubing, adjacent clevises in each pass of tubing having interlocking telescoping ends so that each bight of tubing in the pass can move with respect to the next bight, and the clevises of adjacent passes lying flat against each other so that although each pass is spaced apart thereby from adjacent passes, each pass is nevertheless free to move with respect to the adjacent ones. The attachment of the clevises to the bends completely occludes what would otherwise present some open area to the flow of fluid, and thus all fluid from which or to which heat is being transferred must flow over the finned portions of the tubes.

It is therefore an object of this invention to provide BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a semischematic view in cross-section of a turbine engine, showing the general location of the major elements of a regenerative heat exchanger system;

FIG. 2 is a fragmentary view of the forward heat exchanger taken on line 2--2 of FIG. 1;

FIG. 3 is an enlarged fragmentary view taken on line 3-3 of FIG. 2;

FIG. 4 is a view in the direction of line 4-4 of FIG.

FIG. 5 is an enlarged view similar to FIG. 2; and

FIG. 6 is a perspective view of the telescoping clevis positioning means.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a turbine engine 11 having at the forward end an air compressor 12, which delivers air through an annular forward heat exchanger 13 to a combustion chamber 14. Air enters the front end of the heat exchanger and passes therethrough in the longitudinal direction, discharging rearwardly into the combustion chamber, as shown by the arrows.

The air is mixed with fuel in the combustion chamber and burned, the combustion gases driving a turbine 16 mounted on a shaft 17, which in turn drives the compressor. Afterextraction of work by the turbine, the combustion gases pass into a plenum 18, from which they pass through an annular aft heat exchanger 19 where as much as possible of the remaining heat is removed from the gases, which are then discharged through the exhaust section 21. The forward heat exchanger 13 and the aft heat exchanger 19 are connected by appropriate means (not shown), and form a closed system containing a heat transfer medium, such as a gas or a liquid metal such as sodium or a mixture of sodium and potassium. The engine may be used as a jet engine for flight, or as a stationary engine from which power may be taken off a protruding portion of the shaft, or by other suitable means. The general arrangement thus far is conventional and known in the art.

An annular heat exchanger of this type is commonly formed of a plurality of passes of serpentine tubing longitudinally disposed in the annulus between a pair of cylindrical walls, with the bights of the serpentine extending back and forth across the diametral dimension of the annulus, with appropriate headers at the upstream and downstream ends thereof. If each pass of serpentine tubing were positioned in the annulus in a plane strictly radial to the longitudinal axis, the annulus would be less than completely filled owing to the greater circumference of the outer cylindrical wall. Therefore, although the passes are positioned in the generally radial plane, they are curved therefrom with their outer ends circumferentially displaced from the radial position like curved spokes in a wheel, so that the passes are arcuately nested around the annulus. The actual curve is that of an involute of a cylinder of smaller diameter than the diameter of the inner cylindrical wall. A portion of such a heat exchanger is shown in end view in FIG. 2, and an enlarged fragment of a similar exchanger according to the invention in FIG. 5.

FIG. 2 shows inner and outer annular walls 22 and 23 with a plurality of passes of finned tubing 24 extending therebetween in the manner previously described. Serpentine finned tubing positioned in an annulus in this manner commonly has successive passes disposed with under thermal load. The distance between bights expands or contracts, and the arcuate bends of individual passes flatten or increase their curvature. When the tubing passes are simply installed between annular walls without other restraint, as shown in FIG. 2, such movement often interlocks and damages the thin fins, or imposes strains on the tubing. Further, since it is impossible to install fins on the 180 bends between bights, there is a zone adjacent to each of the cylindrical walls where ambient gas flows only over the bends of the tubes without striking any fins. The finned portions have a pronounced throttling effect on gas flow, and therefore a large proportion of the gas may bypass the fins and flow over the unfinned bends, reducing the efficiency of the heat exchanger.

This invention provides a flat clevis member 26 (shown in FIG. 6) formed of a U-shaped piece of sheet metal, with one end 27 necked down so that it will slide within the larger end of an adjacent clevis member.

One such clevis encloses each 180 bend of the tubing and is brazed, welded, or otherwise securely attached thereto, with its reduced end 27 inserted into the adjacent clevis of the next bend within the same pass of tubing, and with another clevis similarly entering its other end. Each clevis completely encloses the unfinned bend of tubing, up to the beginning of the straight finned portion, but since the clevises telescope within each other there is no restraint of the tubing from its normal thermal movements.

Successive passes of tubing have successive rows of telescoping clevises, as is apparent in FIGS. 3, 4, and 5.

. The thickness dimension of the clevises is so selected that the rows of clevises in alternate passes of tubing lie flat against each other, and slide freely against each other. Thus, although the fins of the tubing are of greater diameter than the thickness of the clevises, al-

ternate bights of tubing are slightly nested between those of the adjacent passes, and are held in their relative positions by the clevises so that no interlocking of fins can occur.

FIG. shows the relationship of several passes of tubing arcuately nested together, bearing in mind that alternate passes are displaced longitudinally from each other by one-half a convolution. The wall thickness of the clevises 26 is much exaggerated in the drawing for clarity of illustration, so that the passes are actually nested together more closely than is apparent. Since the clevises are brazed to the tubing bends, it will be apparent from FIG. 5 that the zones of the annulus adjacent to the inner and outer walls, that is, the portions of the tubing which bear no fins, are nearly completely occluded to the passage of air or other heat transfer medium. Thus, all the fluid is required to transverse the finned portions of the tubing for maximum efficiency of the heat exchanger.

he arrangement of this invention 18 adapted to either the forward heat exchanger of the engine or the aft heat exchanger. That is, it may be used either with an exchanger that gives up its heat to a fluid medium, or with an exchanger which extracts heat from such a medium.

What is claimed is:

1. In an annular heat exchanger having a pair of coaxial annular walls with a plurality of passes of finned tubing disposed between the annular walls for passage of a fluid medium across the finned tubing, each pass of tubing being serpentined in the longitudinal direction into a plurality of bights extending in a generally radial direction between the two walls with bends of adjacent to each wall, the bends of tubing having no fins thereon, the improvement comprising:

a. each of the tubing bends being enclosed within a flat clevis member extending in the generally longitudinal direction;

b. the clevises being attached to the tubing bend so that the fluid medium is occluded from passing across the bend.

2. The combination recited in claim 1, wherein the clevises of each pass of tubing are successively slidably engaged with each other in the longitudinal direction to maintain the bights of each pass in a longitudinal line while allowing thermal movement of individual bights.

3. The combination recited in claim 2, wherein each clevis has one end of reduced dimension telescoping into the larger end of the next adjacent clevis.

4. The combination recited in claim 3, wherein the bights of each pass of tubing have their outer ends displaced from the radial plane in the circumferential direction so that the passes are curved from the radial plane and are arcuately nested within the annular space, the clevises of each pass juxtaposed to the clevises of adjacent passes and freely slidably thereagainst.

5. The combination recited in claim 4, wherein alternate passes of tubing are longitudinally displaced from adjacent passes by half the distance between bights, the fins on the bights being of greater diameter than the overall thickness of the clevises with the fins partially extending between the bights of alternate passes, the longitudinally telescoping and slidable clevises positioning the tubing to allow thermal movement without interlocking of fins. 

1. In an annular heat exchanger having a pair of coaxial annular walls with a plurality of passes of finned tubing disposed between the annular walls for passage of a fluid medium across the finned tubing, each pass of tubing being serpentined in the longitudinal direction into a plurality of bights extending in a generally radial direction between the two walls with bends of 180* adjacent to each wall, the bends of tubing having no fins thereon, the improvement comprising: a. each of the tubing bends being enclosed within a flat clevis member extending in the generally longitudinal direction; b. the clevises being attached to the tubing bend so that the fluid medium is occluded from passing across the bend.
 2. The combination recited in claim 1, wherein the clevises of each pass of tubing are successively slidably engaged with each other in the longitudinal direction to maintain the bights of each pass in a longitudinal line while allowing thermal movement of individual bights.
 3. The combination recited in claim 2, wherein each clevis has one end of reduced dimension telescoping into the larger end oF the next adjacent clevis.
 4. The combination recited in claim 3, wherein the bights of each pass of tubing have their outer ends displaced from the radial plane in the circumferential direction so that the passes are curved from the radial plane and are arcuately nested within the annular space, the clevises of each pass juxtaposed to the clevises of adjacent passes and freely slidably thereagainst.
 5. The combination recited in claim 4, wherein alternate passes of tubing are longitudinally displaced from adjacent passes by half the distance between bights, the fins on the bights being of greater diameter than the overall thickness of the clevises with the fins partially extending between the bights of alternate passes, the longitudinally telescoping and slidable clevises positioning the tubing to allow thermal movement without interlocking of fins. 